Longest string without duplicate characters

This is a topic of Li Kou , At first, I tried to solve it with dynamic programming , Yes, yes , But after reading the solution, I think sliding window is also a wonderful solution , After studying, I made a summary .
1. Traversal string , And define another pointer , Initialize the pointer to the leftmost side of the string
2. Judge whether the character pointed to by the current pointer has appeared in the set .
1） If not , Add this character to the set , And keep the pointer moving to the next character ;
2） If it does , Stop moving .
3. Get the current cut-off string length , And compare with the previous string .

Flow chart ：

The longest string length can be seen intuitively from the process .
Sliding windows is like queues , The first one who comes in is the first to leave after finding repeated characters , Then recycle judgment .

class Solution {
    
    public int lengthOfLongestSubstring(String s) {
    
        Set<Character> set = new HashSet<>();
        int index = 0;// Define the right pointer 
        int max = 0;
        for(int i = 0;i < s.length();i++){
    
            if(i!=0){
    
                set.remove(s.charAt(i-1));
            }
            while(index < s.length()&&!set.contains(s.charAt(index))) {
    
                set.add(s.charAt(index));
                index++;
            }
            max = Math.max(max,index - i);
        }
        return max;
    }
}